-LRB- CNN -RRB- -- Facebook will soon be using your Web browsing to help decide which advertisements you see .

A new Facebook system will use your activity on other websites to send you what Facebook thinks are ads about your current interests . Advertisers will , in effect , be bidding to get their ads in front of you .

Here 's an example : Say a Facebook user visits a travel website and clicks on a page about a vacation package to Las Vegas . If an advertiser has bid on that kind of search , that user could then see ads for discounted trips to Vegas the next time they visit Facebook .

`` By bidding on a specific impression rather than a larger group , advertisers are able to show people more relevant ads while also running more efficient and effective campaigns , '' a Facebook spokeswoman said in a written statement .

The site announced the new system , called Facebook Exchange , to marketers last week . It 's expected to begin rolling out in the next couple of weeks .

Real-time bidding is already widely used across the Internet . In a blog post , Mike Stiles of Atlanta-based social marketing company Vitrue compared the feature to Google 's Ad Words , which pushes an advertiser 's ad in front of users when they search for a keyword that advertiser has chosen .

`` The underlying principle is that users want relevant ads , advertisers do n't want to waste money on misguided ads , and Google wants both users and advertisers to be real happy so they 'll come back again and again , '' he wrote .

Currently , Facebook ads are targeted based on users ' profiles and the companies or other pages they `` like . '' Stiles writes that model will still be available for advertisers , but the new one should be more specific .

Facebook noted that users will be able to opt out of Exchange by going to the site 's About Ads page , by clicking on an `` X '' that appears on the ads themselves or by blocking cookies on their Web browser .

The company statement said Facebook wo n't share any user data with the advertisers and that no advertising controls that users currently have will go away .

How do you feel about Facebook targeting ads ?

Jim Anderson , Vitrue 's chief operating officer , said the new system probably wo n't appear dramatically different to the typical Facebook user .

`` It 's not going to be discernible to most consumers , '' he said . `` Most people wo n't notice any difference or , to the degree they can discern a difference , it will be ` Wow ... this is more relevant to me . '' ''

And while the `` real time '' nature of the new system will enhance relevance , it wo n't be perfect , according to Anderson .

`` It 's possible you might not be served an ad until after you took that trip to Vegas , '' he said , referring to the previous example . `` But without this kind of targeting , you might be served an ad for a trip to Miami , which you were n't considering anyway . ''

As Web giants like Facebook and Google get better at harvesting user activity , using Web searches for advertising is becoming increasingly popular . According to research firm International Data Corporation , more than $ 5 billion in online advertising is expected to go to real-time bidding ads in the United States in 2015 . That 's 27 % of what 's predicted to be spent , up from less than 10 % last year .

Facebook , of course , is increasingly under pressure to demonstrate a sustainable advertising model since its stock went public last month . Anderson predicts the site will continue to diversify how its ads work in the coming months .

It 's sometimes a tricky prospect . It was just revealed that Facebook settled a lawsuit last month by the state of California over its `` Sponsored Stories '' feature . According to reports , Facebook paid $ 10 million to charity after five users claimed the site broke California law when it used their posts in the feature without paying them .

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Facebook Exchange will use Web browsing to target ads

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Browser cookies will let advertisers hyper-focus their offers

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Facebook says users may opt out of the ad model

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`` Real-time bidding '' is already used by Google , others